In many industries today, monitoring systems are used to assess either possible system failures or the affects of environment and other external forces on an object of interest. For example, in the avionics industry, monitoring systems are employed to monitor parameters, such as strains, acceleration, pressures, corrosion, and temperatures at various critical structural locations on aircraft. Similarly, such monitoring systems could be used in the automobile industry to control and monitor everything from on/off occupant controls to drive-train controls and multimedia systems.
Many of these conventional monitoring systems use a plurality of remote devices, such as sensors, actuators, and subsystems that are placed about the object being monitored at the critical locations. Further, many of these conventional monitoring systems include either one or several controllers connected to each of the remote devices for receiving data from the remote devices and sending commands to the remote devices. During operation, the controllers acquire data from the various sensors. The controllers also activate the actuators to perform functions on the object.
Although these conventional monitoring systems provide a way to monitor critical structures of an object, they do have some drawbacks. For example, many of the conventional monitoring systems use dedicated wiring and signal conditioning to connect each of the remote devices to the controller. Additionally, many of the remote devices are typically analog, and data received from the remote devices is typically in analog form.
In many industries today, including the avionics and automotive industries, the complexity of the network may make many conventional monitoring systems impractical for a number of reasons. Specifically, the dedicated wiring and signal conditioning can be expensive, bulky, heavy and hard to install and maintain. This is especially critical in aircraft applications, where weight and size concerns are at the forefront. Further, in the automotive industry, the added wiring may add weight and cost to the car.
Additionally, as stated, many conventional monitoring systems transmit data in an analog format. Typically, analog signals are susceptible to noise introduced into the signals during data transmission. Given that many of the transmitted signals have a low amplitude to start with, this noise can corrupt the signal and decrease the signal to noise ratio levels that cause loss of resolution in the signal. Further, as many of these remote devices are scattered a fair distance from the controller, the electrical lines connecting the remote devices to the controller may be sufficiently long to cause signal degradation due to DC resistance in the wiring.
In light of this, it would be advantageous to replace the dedicated wiring and the analog transmission with a common bus and use digital transmission of data. But, many conventional digital networks suffer from a variety of problems themselves. For example, many existing digital networks demand complicated protocols requiring processors and, thus, forcing unacceptably large or costly remote devices. Processor based sensing devices may also have problems taking samples of analog data, or causing an actuator to take an action, at exactly the right time. Complicated protocols also introduce overhead into the messages on the bus that are not necessary for data acquisition and control. This overhead can severely limit the number of data samples that can be transmitted on the bus. These networks also have other problems. For example, they generally do not support both acquisition and control, and they typically only support short network lengths. Further, these conventional networks typically have bulky network device interfaces, slow network data rates, or a low network device count. Additionally, many computer systems that include digital networks do not operate in a time-deterministic manner. These computer systems generally lack the capability to schedule a trigger command to the network components that repeats or is interpreted and executed with any precision timing.
In light of the foregoing, it would be advantageous to provide a network system that allows network components to digitally communicate over an inexpensive, simple and high-speed, yet robust, network line with a simple, low overhead message protocol, small component size and low wire count. The network system would also advantageously operate without the use of a microcontroller or processor for the network devices. Also, the network system would support both acquisition and control, and be capable of acquiring or converting data simultaneously from the networked components. Further, the network system would allow for high component counts, longer network lines and insure time determinism in a precise manner.